It is frequently desired to collect data at many different points in space in a high temperature environment such as that found within a gas turbine engine. The data collected can include temperature and pressure information. In general, the number of points at which data is to be collected is desired to be as large as possible in order to maximize the information obtained concerning the environment. Thus, a large number of data transducers must be used. The signals generated by the transducers must be transmitted from each to a common recording or processing station. In the case of electrical signals, this requires that a separate transmitting wire or pair of wires be provided for each transducer. Further, if the transducers are to be located on a rotating component of the gas turbine engine, additional factors must be accommodated: (1) The signals carried by the rotating wires must be transmitted to a nonrotating processing station. This is generally accomplished by utilized slip rings, one for each wire, or by utilizing a radio telemetry transmitter. (2) The transmitting wires can experience centrifugal forces in excess of 10,000 g's; consequently, the wires must be securely fastened along their entire lengths to the rotating component to prevent movement of the wires as well as mechanical damage to them. (3) The high centrifugal forces involved necessitate that the transmitting wires be arranged in a symmetrical manner to achieve nearly perfect dynamic balance. The accommodation of all of these three factors requires a duplication in both effort and material. Furthermore, sometimes engine design choices and space limitations make it impossible to route the necessary number of wires from the rotating transducers to a point where the signals are transferred from the wires to the collection station. Thus, a frequent result is that the number of wires is reduced by eliminating transducers.
It is also desirable to obtain data by means of transducers located within a hostile environment, such as within a pressurized steam containment vessel. In such a vessel, it is desirable to minimize the number of electrical conduits which penetrate through holes in the wall of the vessel because the holes decrease the strength of the walls and each hole provides an additional potential site for leakage to occur.
In all cases generally, if a multiplexer is used to multiplex the signals produced by numerous transducers onto a single output channel, energy must be delivered to the multiplexer to sustain its operation. The energy delivery can encounter the usual problems of delivering electricity to a rapidly rotating shaft in a gas turbine engine or to the interior of a pressurized steam containment vessel.